Abstract

Surface textures are widely used to enhance absorption in an optical sheet by scattering weakly absorbed light into totally internally reflected modes. This study, which is based on ray-tracing studies of crystalline silicon solar cells with periodic geometric textures, investigates how the distribution of scatter influences absorption enhancement. The distribution of scatter is found to depend on the topology of texture facets as well as on the direction of incident light. Examples of the scatter characteristics in sheets textured with inverted pyramids, grooves, and perpendicular grooves are given. Broadly scattering textures are found to develop random scatter consistently only when exposed to isotropically incident band-gap wavelengths. Although broadband absorption enhancement from a geometric texture is affected by whether scatter is two or three dimensional, the fraction of rays blocked by the texture at early scatter stages is more important. Reasons are given as to why there may be geometric textures that enhance broadband absorption more than the randomizing texture under isotropic incidence.

References

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Table 1

Variation of Path-Length Enhancement with Incident Angle for a Class I Texturea

Inclination (deg)

Azimuth (deg)

0

15

30

45

60

75

90

0

76

15

65

63

60

60

61

50

66

30

66

72

65

59

55

54

43

45

64

64

61

44

47

41

58

60

17

25

27

56

63

38

33

75

19

28

46

79

81

74

57

a This distribution is from scatter produced by perpendicularly grooved 〈111〉facets on silicon for one particular texture poriod:substrate thickness ratio. Inclination is from the surface normal, and the azimuth is zero when directed across the grooves. The hemispherically averaged enhancement over these angles, equivalent to that from isotropic incidence, is 52.3 for any period thickness ratio. For a randomizing texture, Pn = 51.0 at all incident angles.

Table 2

Variation of Path-Length Enhancement with Incident Angle for a Class II Texturea

Inclination (deg)

Azimuth (deg)

0

15

30

45

60

75

90

0

4

15

4

4

9

9

4

5

7

30

6

6

4

6

7

5

3

45

4

6

3

6

5

7

6

60

7

6

7

10

9

21

20

75

4

7

16

20

34

7

35

a This distribution is from scatter produced by grooved 〈111〉 facets (top)/planar (rear) on silicon. As in Table 1, this enhancement varies with the period thickness ratio, and the value for Pn from isotropic incidence does not. In contrast to class I texture, Pn from isotropic incidence depends on class II texture topology. Inclination is from the surface normal, and the azimuth is zero when directed along the grooves.

Tables (2)

Table 1

Variation of Path-Length Enhancement with Incident Angle for a Class I Texturea

Inclination (deg)

Azimuth (deg)

0

15

30

45

60

75

90

0

76

15

65

63

60

60

61

50

66

30

66

72

65

59

55

54

43

45

64

64

61

44

47

41

58

60

17

25

27

56

63

38

33

75

19

28

46

79

81

74

57

a This distribution is from scatter produced by perpendicularly grooved 〈111〉facets on silicon for one particular texture poriod:substrate thickness ratio. Inclination is from the surface normal, and the azimuth is zero when directed across the grooves. The hemispherically averaged enhancement over these angles, equivalent to that from isotropic incidence, is 52.3 for any period thickness ratio. For a randomizing texture, Pn = 51.0 at all incident angles.

Table 2

Variation of Path-Length Enhancement with Incident Angle for a Class II Texturea

Inclination (deg)

Azimuth (deg)

0

15

30

45

60

75

90

0

4

15

4

4

9

9

4

5

7

30

6

6

4

6

7

5

3

45

4

6

3

6

5

7

6

60

7

6

7

10

9

21

20

75

4

7

16

20

34

7

35

a This distribution is from scatter produced by grooved 〈111〉 facets (top)/planar (rear) on silicon. As in Table 1, this enhancement varies with the period thickness ratio, and the value for Pn from isotropic incidence does not. In contrast to class I texture, Pn from isotropic incidence depends on class II texture topology. Inclination is from the surface normal, and the azimuth is zero when directed along the grooves.